Patterned photovoltaic cell

ABSTRACT

Patterned photovoltaic cells, as well as related components and methods, are disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 60/637,843, filed on Dec. 20, 2004, and U.S. Provisional ApplicationSer. No. 60/638,070, filed on Dec. 21, 2004. These applications areincorporated herein by reference.

TECHNICAL FIELD

This invention relates to patterned photovoltaic cells, as well asrelated components and methods.

BACKGROUND

Photovoltaic cells, sometimes called solar cells, can convert light,such as sunlight, into electrical energy. One type of photovoltaic cellis a dye-sensitized solar cell (DSSC).

Referring to FIG. 1, a DSSC 100 includes a charge carrier layer 140(e.g., including an electrolyte, such as an iodide/iodine solution) anda photoactive layer 150 (e.g., including a semiconductor material, suchas TiO₂ particles) disposed between an electrode 101 and a counterelectrode 111. Photoactive layer 150 also includes a photosensitizingagent, such as a dye. In general, the photosensitizing agent is capableof absorbing photons within a wavelength range of operation (e.g.,within the solar spectrum). Electrode 101 includes a substrate 170(e.g., a glass or polymer substrate) and an electrically conductivelayer 160 (e.g., an ITO layer or tin oxide layer) disposed on an innersurface 172 of substrate 170. Counter electrode 111 includes a substrate110, an electrically conductive layer 120 (e.g., ITO layer or tin oxidelayer), and a catalytic layer 130 (e.g., containing platinum), whichcatalyzes a redox reaction in charge carrier layer 140. Electricallyconductive layer 120 is disposed on an inner surface 112 of substrate110, while catalytic layer 130 is disposed on a surface 122 ofelectrically conductive layer 120. Electrode 101 and counter electrode111 are connected by wires across an external electrical load 180.

During operation, in response to illumination by radiation (e.g., in thesolar spectrum), DSSC 100 undergoes cycles of excitation, oxidation, andreduction that produce a flow of electrons across load 180. Incidentlight excites photosensitizing agent molecules in photoactive layer 150.The photoexcited photosensitizing agent molecules then inject electronsinto the conduction band of the semiconductor in photoactive layer 150,which leaves the photosensitizing agent molecules oxidized. The injectedelectrons flow through the semiconductor material, to electricallyconductive layer 160, then to external load 180. After flowing throughexternal load 180, the electrons flow to layer 120, then to layer 130and subsequently to layer 140, where the electrons reduce theelectrolyte material in charge carrier layer 140 at catalytic layer 130.The reduced electrolyte can then reduce the oxidized photosensitizingagent molecules back to their neutral state. The electrolyte in layer140 can act as a redox mediator to control the flow of electrons fromcounter electrode 111 to working electrode 101. This cycle ofexcitation, oxidation, and reduction is repeated to provide continuouselectrical energy to external load 180.

SUMMARY

This invention relates to patterned photovoltaic cells, as well asrelated components and methods.

In certain instances, it may be desirable for a photovoltaic cell tohave a particular appearance. As an example, in embodiments in which aphotovoltaic cell is incorporated as part of military wear, it may bedesirable for the photovoltaic cell to have the appearance of acamouflage pattern. As another example, in embodiments in which aphotovoltaic cell is incorporated as part of a roof, it may be desirablefor the photovoltaic cell to have the appearance of a roof tile patternor a shingle pattern.

In one aspect, the invention features a method that includes combining aplurality of dyes with a material (e.g., a semiconductor) to form aphotoactive layer in which the plurality of dyes are arranged in apattern, and disposing the photoactive layer between two electrodes toprovide a photovoltaic cell.

In another aspect, the invention features a photovoltaic cell thatincludes two electrodes and a photoactive layer between the electrodes.The photoactive layer includes a plurality of dyes arranged in apattern.

In a further aspect, the invention features a module including multiplephotovoltaic cells that are electrically connected (e.g., with some ofthe cells in series and/or with some of the cells in parallel). At leastsome of the photovoltaic cells include two electrodes and a photoactivelayer between the electrodes, where the photoactive layer includes aplurality of dyes arranged in a pattern.

Embodiments can include one or more of the following features.

The pattern can be, for example, a camouflage pattern, a roof tilepattern, a shingle pattern. In some embodiments, the pattern provided bythe photovoltaic cell can define the pattern of the housing a portableelectronic device (e.g., a laptop computer, a cell phone). In certainembodiments, the pattern provided by the photovoltaic cell can definethe pattern on the body of an automobile.

The photoactive layer can include at least two (e.g., at least three, atleast four, at least five, at least six, at least seven, at least eight)different dyes. At least some of the dyes (e.g., at least two of thedyes, at least three of the dyes, at least four of the dyes) can have adifferent color. For example, each of the dyes can have a differentcolor.

The dyes can be applied to the material (e.g., semiconductor material)using silk screening, ink jet printing, or gravure printing.

The material with which the dyes are combined can be a semiconductormaterial. In some embodiments, the semiconductor material can betitania, such as sintered titania. Generally, the semiconductor materialis in the form of nanoparticles.

The photovoltaic cell can further include a substrate, such as a polymersubstrate, that supports the photoactive layer. In certain embodiments,the substrate can be formed of polyethylene terephthalate, polyethylenenaphthalate, polyethylene, polypropylene, polyamide, polymethacrylate,polycarbonate, and/or polyurethane.

The photovoltaic cell can be a dye sensitized solar cell.

In another aspect, the invention features a method that includescombining a plurality of polymer compositions with a material (e.g., anelectron acceptor) to form a photoactive layer in which the plurality ofpolymer compositions are arranged in a pattern, and disposing thephotoactive layer between two electrodes to provide a photovoltaic cell.

In an additional aspect, the invention features a photovoltaic cell thatincludes two electrodes and a photoactive layer between the electrodes.The photoactive layer includes a plurality of polymer compositionsarranged in a pattern.

In a further aspect, the invention features a module including multiplephotovoltaic cells that are electrically connected (e.g., with some ofthe cells in series and/or with some of the cells in parallel). At leastsome of the photovoltaic cells include two electrodes and a photoactivelayer between the electrodes, where the photoactive layer includes aplurality of polymer compositions arranged in a pattern.

Embodiments can include one or more of the following features.

The pattern can be, for example, a camouflage pattern, a roof tilepattern, a shingle pattern. In some embodiments, the pattern provided bythe photovoltaic cell can define the pattern of the housing a portableelectronic device (e.g., a laptop computer, a cell phone). In certainembodiments, the pattern provided by the photovoltaic cell can definethe pattern on the body of an automobile.

The photoactive layer can include at least two (e.g., at least three, atleast four, at least five, at least six, at least seven, at least eight)different polymer compositions. At least some of the polymercompositions (e.g., at least two of the polymer compositions, at leastthree of the polymer compositions, at least four of the polymercompositions) can have a different color. For example, each of thepolymer compositions can have a different color.

The polymer compositions can be combined with the material (e.g.,electron acceptor) using silk screening, ink jet printing, or gravureprinting.

In some of the embodiments, the polymer composition(s) contained in thephotoactive layer can include one or more of discotic liquid crystalpolymers, one or more polythiophenes, one or more polyphenylenes, one ormore poly(phenylene-vinylene)s, one or more polythienylvinylenes, and/orone or more polyisothianaphthalenes.

The material with which the polymer compositions are combined can be anelectron acceptor material. The electron acceptor material can be formedof fullerenes, inorganic nanoparticles, oxadiazoles, discotic liquidcrystals, carbon nanorods, inorganic nanorods, polymers containing CNgroups, and/or polymers containing CF₃ groups.

The photovoltaic cell can further include a substrate, such as a polymersubstrate, that supports the photoactive layer. The substrate can beformed of a polyethylene terephthalate, a polyethylene naphthalate, apolyethylene, a polypropylene, a polyamide, a polymethacrylate, apolycarbonate, and/or a polyurethane.

In another aspect, the invention features a formulation containingcis-RuLL′(NCS)₂ and an organic solvent, in which L can include a first2,2′-bipyridyl and L′ can include a second 2,2′-bipyridyl. The organicsolvent can be selected from the group consisting of g-butyrolactone(GBL), 1-methoxy-2-propanol (MP), N,N-dimethyl formamide,N,N-dimethylacetamide, propylene glycol phenyl ether, and a mixturethereof.

In still another aspect, the invention features a formulation containinga dye and a thickening agent.

In an additional aspect, the invention features a method that includesdisposing a formulation comprising cis-RuLL′(NCS)₂ and a first organicsolvent on a first material to form a photoactive layer, and disposingthe photoactive layer between two electrodes to provide a photovoltaiccell. L includes a first 2,2′-bipyridyl and L′ includes a second2,2′-bipyridyl. The first organic solvent is selected from the groupconsisting of g-butyrolactone, 1-methoxy-2-propanol, N,N-dimethylformamide, N,N-dimethylacetamide, propylene glycol phenyl ether, and amixture thereof.

In a further aspect, the invention features a method that includesdisposing a formulation containing a dye and a thickening agent on afirst material to form a photoactive layer, and disposing thephotoactive layer between two electrodes to provide a photovoltaic cell.

Embodiments can include one or more of the following features.

The first 2,2′-bipyridyl can be the same as the second 2,2′-bipyridyl.

L can include 4,4′-dicarboxylic acid-2,2′-bipyridyl and L′ can include4,4′-dinonyl-2,2′-bipyridyl.

The formulation can further include about 1 wt % to about 20 wt % (e.g.,about 5 wt % to about 15 wt %, or about 12 wt %) of a thickening agent.Exemplary thickening agents include fumed silica particles andpoly(propylene glycol) (PPG). Fumed silica particles can be hydrophobic.For example, a surface of the fumed silica particles can be modifiedwith hydrophobic groups (e.g., poly(dimethyl siloxane) moieties).

The organic solvent can include a mixture of g-butyrolactone and1-methoxy-2-propanol (e.g., at a ratio of about 1:5 vol./vol. to about1:10 vol./vol.).

The formulation can include a mixture of g-butyrolactone,1-methoxy-2-propanol, and poly(propylene glycol) (e.g., at a ratio ofabout 1:5:2 vol./vol./vol.).

The formulation can include at least about 5 mM cis-RuLL′(NCS)₂ (e.g.,at least about 20 mM cis-RuLL′(NCS)₂, at least about 30 mMcis-RuLL′(NCS)₂, at least about 40 mM cis-RuLL′(NCS)₂, or at least about60 mM cis-RuLL′(NCS)₂).

The method can further include substantially removing the thickeningagent by washing the photoactive layer with a second organic solvent(e.g., an alcohol).

65 mg of cis-RuLL′(NCS)₂ can be absorbed onto 1 g of the first materialin at most about 5 minutes (e.g., at most about 4 minutes, at most about3 minutes, at most about 2 minutes, or at most about 1 minute).

The first material can include a semiconductor material or an electronacceptor material.

Other features and advantages of the invention will be apparent from thedescription, drawings and claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an embodiment of a photovoltaiccell.

FIG. 2 is a top view of an embodiment of a patterned photoactive layerof a photovoltaic cell.

FIG. 3 is a cross-sectional view of the photovoltaic cell of FIG. 2.

FIG. 4 is a schematic of a system containing multiple photovoltaic cellselectrically connected in series.

FIG. 5 is a schematic of a system containing multiple photovoltaic cellselectrically connected in parallel.

FIG. 6 illustrates an embodiment of a process for manufacturing apatterned photovoltaic cell.

FIG. 7 is a top view of an embodiment of a patterned photoactive layerof a photovoltaic cell.

FIG. 8 is a cross-sectional view of the photovoltaic cell of FIG. 7.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

A patterned photovoltaic cell can have the appearance of any desiredpattern. The pattern can be, for example, a camouflage pattern, a rooftile pattern, a shingle pattern. In some embodiments, the patternprovided by the photovoltaic cell can define the pattern of the housinga portable electronic device (e.g., a laptop computer, a cell phone). Incertain embodiments, the pattern provided by the photovoltaic cell candefine the pattern on the body of an automobile. In general, a patterncan be formed by using multiple photosensitizing agents (dyes) ofdifferent color in the photoactive layer of a DSSC.

FIG. 2 is a top view of a photoactive layer 250 of a DSSC 200, and FIG.3 is a cross-sectional view of DSSC 200. Photoactive layer 250 includesregions 251-256 that form a pattern. The pattern results from at leastsome of the regions being of different color. As an example, in someembodiments, each of regions 251-256 has a different color. Moregenerally, however, at least two of regions (e.g., at least three ofregions, at least four of the regions, at least five of the regions)251-256 have a different color.

In general, the color of each region 251-156 is determined by theparticular dye (or combination of dyes) contained within the givenregion. Examples of dyes include black dyes (e.g.,tris(isothiocyanato)-ruthenium(II)-2,2′:6′,2″-terpyridine-4,4′,4″-tricarboxylic acid,tris-tetrabutylammonium salt), orange dyes (e.g.,tris(2,2′-bipyridyl-4,4′-dicarboxylato) ruthenium (II) dichloride,purple dyes (e.g.,cis-bis(isothiocyanato)bis-(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II)), red dyes (e.g., an eosin), green dyes (e.g., a merocyanine) andblue dyes (e.g., a cyanine). Examples of additional dyes includecyanines, xanthenes, anthraquinones, merocyanines, phenoxazinones,indolines, thiophenes, coumarins, anthocyanines, porphyrins,phthalocyanines, squarates, squarylium dyes, and certainmetal-containing dyes. Combinations of dyes can also be used within agiven region so that a given region can include more than one (e.g.,two, three, four, five, six, seven) different dyes.

In some embodiments, photoactive layer 250 can include a dye having aformula cis-RuLL′(NCS)₂, in which L can include a first 2,2′-bipyridyland L′ can include a second 2,2′-bipyridyl. The first 2,2′-bipyridyl canbe the same as or can be different from the second 2,2′-bipyridyl. Theterm “2,2′-bipyridal” mentioned herein includes both substituted andunsubstituted moieties. Examples of substituents include C₁-C₁₀ alkyl,C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₃-C₈ cycloalkyl, C₅-C₈ cycloalkenyl,C₁-C₁₀ alkoxy, aryl, aryloxy, heteroaryl, heteroaryloxy, amino, C₁-C₁₀alkylamino, C₁-C₂₀ dialkylamino, arylamino, diarylamino,heteroarylamino, diheteroarylamino, C₁-C₁₀ alkylsulfonyl, arylsulfonyl,heteroarylsulfonyl, C₁-C₁₀ alkylsulfonamide, arylsulfonamide,heteroarylsulfonamide, hydroxyl, halogen, mercapto, C₁-C₁₀alkylmercapto, arylmercapto, cyano, nitro, acyl, acyloxy, carboxyl,amido, carbamoyl, and carboxylic ester. Cycloalkyl, heterocycloalkyl,aryl, and heteroaryl also include fused groups.

An example of cis-RuLL′(NCS)₂ is cis-Ru(4,4′-dicarboxylicacid-2,2′-bipyridyl)(4,4′-dinonyl-2,2′-bipyridyl)(NCS)₂ (Z907). Incertain embodiments, Z907 is first dissolved in a suitable organicsolvent to form a dye solution. The organic solvent typically has lowvapor pressure (e.g., <10 mmHg at 20° C.), good dye solubility (e.g.,dissolving more than 5 mM of the dye), high permittivity and wettabilityto the semiconductor material in a photoactive layer (e.g., TiO₂nanoparticles), thereby facilitating dye absorbance to the semiconductormaterial and reducing the dyeing time. Examples of such organic solventsinclude g-butyrolactone, 1-methoxy-2-propanol, N,N-dimethyl formamide,N,N-dimethylacetamide, propylene glycol phenyl ether, and a mixturethereof. The dye solution can then be applied to a semiconductormaterial by one or more methods disclosed herein. The dyeing processusing such a dye solution can have a relatively short dyeing time. Incertain embodiments, by using a dyeing solution mentioned above, 65 mgof Z907 can be absorbed onto 1 g of the semiconductor material in atmost about 5 minutes, (e.g., at most about 4 minutes, at most about 3minutes, at most about 2 minutes, or at most about 1 minute).

In some embodiments, a thickening agent can be added to a solutioncontaining a dye (e.g., a ruthenium based dye such as Z907 or an organicdye). The thickening agent can reduce the dyeing time. It can also beused to adjust the rheology (e.g., the viscosity) of the dye solution byusing different concentrations. Exemplary thickening agents includedispensible fumed silica particles and poly(propylene glycol). After thedye is absorbed onto a semiconductor material, the thickening agent canbe optionally removed by washing the semiconductor material with anorganic solvent (e.g., ethanol or 1-methoxy-2-propanol).

In some embodiments, the fumed silica particles can be modified to forma hydrophobic surface. For example, the surface of the fumed silicaparticles can be modified with poly(dimethyl siloxane) moieties. Anexample of such a hydrophobic silica is CAB-O-SIL TS-720 manufactured byCABOT CORPORATION. Hydrophobic silica particles can improve the thermalstability of a photovoltaic cell. Without wishing to be bound by theory,it is believed that hydrophobic silica particles can minimize thecontact between the dye and the electrolyte in the photovoltaic cell,thereby reducing dye desorption.

Photoactive layer 250 also includes an additional material, such as asemiconductor material, that is associated with the dyes. Examples ofsemiconductor materials include materials having the formula M_(x)O_(y),where M may be, for example, titanium, zirconium, tungsten, niobium,lanthanum, tantalum, terbium, or tin and x and y are integers greaterthan zero. Other suitable materials include sulfides, selenides,tellurides, and oxides of titanium, zirconium, tungsten, niobium,lanthanum, tantalum, terbium, tin, or combinations thereof. For example,TiO₂, SrTiO₃, CaTiO₃, ZrO₂, WO₃, La₂O₃, Nb₂O₅, SnO₂, sodium titanate,cadmium selenide (CdSe), cadmium sulphides, and potassium niobate may besuitable materials.

Typically, the semiconductor material contained within layer 250 is inthe form of nanoparticles. In some embodiments, the nanoparticles havean average size between about two nm and about 100 nm (e.g., betweenabout 10 nm and 40 nm, such as about 20 nm).

The nanoparticles can be interconnected, for example, by hightemperature sintering, or by a reactive polymeric linking agent, such aspoly(n-butyl titanate). A polymeric linking agent can enable thefabrication of an interconnected nanoparticle layer at relatively lowtemperatures (e.g., less than about 300° C.) and in some embodiments atroom temperature. The relatively low temperature interconnection processmay be amenable to continuous manufacturing processes using polymersubstrates.

The interconnected nanoparticles are generally photosensitized by thedye(s). The dyes facilitates conversion of incident light intoelectricity to produce the desired photovoltaic effect. It is believedthat a dye absorbs incident light resulting in the excitation ofelectrons in the dye. The energy of the excited electrons is thentransferred from the excitation levels of the dye into a conduction bandof the interconnected nanoparticles. This electron transfer results inan effective separation of charge and the desired photovoltaic effect.Accordingly, the electrons in the conduction band of the interconnectednanoparticles are made available to drive an external load.

The dye(s) can be sorbed (e.g., chemisorbed and/or physisorbed) on thenanoparticles. A dye can be selected, for example, based on its abilityto absorb photons in a wavelength range of operation (e.g., within thevisible spectrum), its ability to produce free electrons (or electronholes) in a conduction band of the nanoparticles, its effectiveness incomplexing with or sorbing to the nanoparticles, and/or its color.

Turning now to other components of DSSC 200, the composition andthickness of electrically conductive layer 220 is generally selectedbased on desired electrical conductivity, optical properties, and/ormechanical properties of the layer. In some embodiments, layer 220 istransparent. Examples of transparent materials suitable for forming sucha layer include certain metal oxides, such as indium tin oxide (ITO),tin oxide, and a fluorine-doped tin oxide. In some embodiments,electrically conductive layer 220 can be formed of a foil (e.g., atitanium foil). Electrically conductive layer 220 may be, for example,between about 100 nm and 500 nm thick, (e.g., between about 150 nm and300 nm thick).

In embodiments where counter electrode 211 is not transparent,electrically conductive layer 220 can be opaque (i.e., can transmit lessthan about 10% of the visible spectrum energy incident thereon). Forexample, layer 220 can be formed from a continuous layer of an opaquemetal, such as copper, aluminum, indium, or gold.

In some embodiments, electrically conductive layer 220 can include adiscontinuous layer of a conductive material. For example, electricallyconductive layer 220 can include an electrically conducting mesh.Suitable mesh materials include metals, such as palladium, titanium,platinum, stainless steels and alloys thereof. In some embodiments, themesh material includes a metal wire. The electrically conductive meshmaterial can also include an electrically insulating material that hasbeen coated with an electrically conducting material, such as a metal.The electrically insulating material can include a fiber, such as atextile fiber or monofilament. Examples of fibers include syntheticpolymeric fibers (e.g., nylons) and natural fibers (e.g., flax, cotton,wool, and silk). The mesh electrode can be flexible to facilitate, forexample, formation of the DSSC by a continuous manufacturing process.Photovoltaic cells having mesh electrodes are disclosed, for example, inco-pending U.S. Patent Application Publication No. 2003/0230337, U.S.Patent Application Publication No. 2004/0187911, and InternationalPatent Application Publication Number WO 03/04117, each of which ishereby incorporated by reference.

The mesh electrode may take a wide variety of forms with respect to, forexample, wire (or fiber) diameters and mesh densities (i.e., the numberof wires (or fibers) per unit area of the mesh). The mesh can be, forexample, regular or irregular, with any number of opening shapes. Meshform factors (such as, e.g., wire diameter and mesh density) can bechosen, for example, based on the conductivity of the wire (or fibers)of the mesh, the desired optical transmissivity, flexibility, and/ormechanical strength. Typically, the mesh electrode includes a wire (orfiber) mesh with an average wire (or fiber) diameter in the range fromabout one micron to about 400 microns, and an average open area betweenwires (or fibers) in the range from about 60% to about 95%.

Catalyst layer 230 is generally formed of a material that can catalyze aredox reaction in the charge carrier layer positioned below. Examples ofmaterials from which catalyst layer can be formed include platinum andpoly(3,4-ethylenedioxythiophene) (PEDOT). PEDOT layers are discussed inU.S. Ser. No. 60/495,302, which is hereby incorporated by reference.Materials can be selected based on criteria such as, e.g., theircompatibility with manufacturing processes, long term stability, andoptical properties. In general, the catalyst layer is substantiallytransparent. However, in certain embodiments, (e.g., embodiments inwhich the cathodes are substantially transparent) the catalyst layer canbe substantially opaque.

Substrate 210 can be formed from a mechanically-flexible material, suchas a flexible polymer, or a rigid material, such as a glass. Examples ofpolymers that can be used to form a flexible substrate includepolyethylene naphthalates (PEN), polyethylene terephthalates (PET),polyethyelenes, polypropylenes, polyamides, polymethylmethacrylate,polycarbonate, and/or polyurethanes. Flexible substrates can facilitatecontinuous manufacturing processes such as web-based coating andlamination.

The thickness of substrate 210 can vary as desired. Typically, substratethickness and type are selected to provide mechanical support sufficientfor the DSSC to withstand the rigors of manufacturing, deployment, anduse. Substrate 210 can have a thickness of from about six microns toabout 5,000 microns (e.g., from about 6 microns to about 50 microns,from about 50 microns to about 5,000 microns, from about 100 microns toabout 1,000 microns).

In embodiments where the counter electrode is transparent, substrate 210is formed from a transparent material. For example, substrate 210 can beformed from a transparent glass or polymer, such as a silica-based glassor a polymer, such as those listed above. In such embodiments,electrically conductive layer 220 should also be transparent.

Substrate 270 and electrically conductive layer 260 can be similar tosubstrate 210 and electrically conductive layer 220, respectively. Forexample, substrate 270 can be formed from the same materials and canhave the same thickness as substrate 210. In some embodiments however,it may be desirable for substrate 270 to be different from 210 in one ormore aspects. For example, where the DSSC is manufactured using aprocess that places different stresses on the different substrates, itmay be desirable for substrate 270 to be more or less mechanicallyrobust than substrate 210. Accordingly, substrate 270 may be formed froma different material, or may have a different thickness that substrate210. Furthermore, in embodiments where only one substrate is exposed toan illumination source during use, it is not necessary for bothsubstrates and/or electrically conducting layers to be transparent.Accordingly, one of substrates and/or corresponding electricallyconducting layer can be opaque.

As discussed previously, charge carrier layer 240 includes a materialthat facilitates the transfer of electrical charge from a groundpotential or a current source to photoactive layer 260. A general classof suitable charge carrier materials include solvent-based liquidelectrolytes, polyelectrolytes, polymeric electrolytes, solidelectrolytes, n-type and p-type transporting materials (e.g., conductingpolymers) and gel electrolytes. Other choices for charge carrier mediaare possible. For example, the charge carrier layer can include alithium salt that has the formula LiX, where X is an iodide, bromide,chloride, perchlorate, thiocyanate, trifluoromethyl sulfonate, orhexafluorophosphate.

The charge carrier media typically includes a redox system. Suitableredox systems may include organic and/or inorganic redox systems.Examples of such systems include cerium(III) sulphate/cerium(IV), sodiumbromide/bromine, lithium iodide/iodine, Fe²⁺/Fe³⁺, Co²⁺/Co³⁺, andviologens. Furthermore, an electrolyte solution may have the formulaM_(i)X_(j), where i and j are greater than or equal to one, where X isan anion, and M is lithium, copper, barium, zinc, nickel, a lanthanide,cobalt, calcium, aluminum, or magnesium. Suitable anions includechloride, perchlorate, thiocyanate, trifluoromethyl sulfonate, andhexafluorophosphate.

In some embodiments, the charge carrier media includes a polymericelectrolyte. For example, the polymeric electrolyte can includepoly(vinyl imidazolium halide) and lithium iodide and/or polyvinylpyridinium salts. In embodiments, the charge carrier media can include asolid electrolyte, such as lithium iodide, pyridimum iodide, and/orsubstituted imidazolium iodide.

The charge carrier media can include various types of polymericpolyelectrolytes. For example, suitable polyelectrolytes can includebetween about 5% and about 95% (e.g., 5-60%, 5-40%, or 5-20%) by weightof a polymer, e.g., an ion-conducting polymer, and about 5% to about 95%(e.g., about 35-95%, 60-95%, or 80-95%) by weight of a plasticizer,about 0.05 M to about 10 M of a redox electrolyte of organic orinorganic iodides (e.g., about 0.05-2 M, 0.05-1 M, or 0.05-0.5 M), andabout 0.01 M to about 1 M (e.g., about 0.05-0.5 M, 0.05-0.2 M, or0.05-0.1 M) of iodine. The ion-conducting polymer may include, forexample, polyethylene oxide (PEO), polyacrylonitrile (PAN),polymethylmethacrylate (PMMA), polyethers, and polyphenols. Examples ofsuitable plasticizers include ethyl carbonate, propylene carbonate,mixtures of carbonates, organic phosphates, butyrolactone, anddialkylphthalates.

Multiple photovoltaic cells can be electrically connected to form aphotovoltaic system. As an example, FIG. 4 is a schematic of aphotovoltaic system 50 having a module 51 containing photovoltaic cells52. Cells 52 are electrically connected in series, and system 50 iselectrically connected to a load. As another example, FIG. 5 is aschematic of a photovoltaic system 60 having a module 61 that containsphotovoltaic cells 62. Cells 62 are electrically connected in parallel,and system 60 is electrically connected to a load. In some embodiments,some (e.g., all) of the photovoltaic cells in a photovoltaic system canhave one or more common substrates. In certain embodiments, somephotovoltaic cells in a photovoltaic system are electrically connectedin series, and some of the photovoltaic cells in the photovoltaic systemare electrically connected in parallel.

FIG. 6 shows a process (a roll-to-roll process) 300 for manufacturing apatterned photovoltaic cell by advancing a substrate 310 between rollers315. Substrate 310 can be advanced between rollers 315 continuously,periodically, or irregularly during a manufacturing run.

An electrically conductive layer 320 (e.g., a titanium foil) is attachedto substrate 310 adjacent location 312.

An interconnected nanoparticle material is then formed on theelectrically conductive layer adjacent location 313. The interconnectednanoparticle material can be formed by applying a solution containing apolymeric linking agent (e.g., poly(n-butyl titanate)) and metal oxidenanoparticles (e.g., titania). In some embodiments, the polymericlinking agent and the metal oxide nanoparticles are separately appliedto form the interconnected nanoparticle material. The polymeric linkingagent and metal oxide nanoparticles can be heated (e.g., in an ovenpresent in the system used in the roll-to-roll process) to form theinterconnected nanoparticle material.

A plurality of dyes is then applied to the interconnected nanoparticlematerial adjacent location 335 to form a patterned photoactive layer.The dyes can be applied using known methods, including those notedabove. In some embodiments, the different dyes are simultaneouslyapplied to the interconnected nanoparticle material (e.g., using ink jetprinting). In certain embodiments, multiple stations are used, with adifferent dye being applied to the interconnected nanoparticle material(e.g., using ink jet printing) at each station. Combinations of thesemethods can also be used.

A charge carrier layer is deposited onto the patterned photoactive layeradjacent location 316. The charge carrier layer can be deposited usingknown techniques, such as those noted above.

An electrically conductive layer 360 (e.g., ITO) is attached tosubstrate 370 adjacent location 319.

A catalyst layer precursor is deposited on electrically conductive layer360 adjacent location 318. The catalyst layer precursor can be depositedon electrically conductive layer 360 using, for example, electrochemicaldeposition using chloroplatinic acid in an electrochemical cell, orpyrolysis of a coating containing a platinum compound (e.g.,chloroplatinic acid). In general, the catalyst layer precursor can bedeposited using known coating techniques, such as spin coating, dipcoating, knife coating, bar coating, spray coating, roller coating, slotcoating, gravure coating, screen coating, and/or ink jet printing. Thecatalyst layer precursor is then heated (e.g., in an oven present in thesystem used in the roll-to-roll process) to form the catalyst layer. Insome embodiments, electrically conductive material 360 can be at leastpartially coated with the catalyst layer before attaching to advancingsubstrate 370. In certain embodiments, the catalyst layer is applieddirectly to electrically conductive layer 360 (e.g., without thepresence of a precursor).

While certain embodiments have been described, other embodiments arepossible.

As an example, while embodiments of patterned DSSCs have been described,other types of patterned photovoltaic cells (e.g., patterned polymerorganic photovoltaic cells) are also possible. For example, FIG. 7 is atop view of a photoactive layer 550 of a polymer organic photovoltaiccell 500, and FIG. 8 is a cross-sectional view of cell 500. Cell 500includes a transparent substrate 510, a cathode 520, a hole carrierlayer 530, a photoactive layer (containing an electron acceptor materialand an electron donor material) 540, a hole blocking layer 550, an anode560, and a substrate 570.

Photoactive layer 540 includes multiple regions 541-546. Two or more ofthe different regions of photoactive layer 540 can each include adifferent polymer composition as the electron donor material within thatregion. At least two (e.g., at least three, at least four, at leastfive) of the polymer compositions have a different color so that cell500 appears patterned (e.g., having one of the patterns noted above).Examples of polymer compositions include discotic liquid crystalpolymers, polythiophenes, polyphenylenes, poly(phenylene-vinylene)s,polythienylvinylenes, polyisothianaphthalenes, and combinations thereof.

Examples of the electron acceptor materials that can be used inphotoactive layer 540 include fullerenes, inorganic nanoparticles (e.g.,nanoparticles formed of zinc oxide, tungsten oxide, indium phosphide,cadmium selenide and/or lead sulphide), oxadiazoles, discotic liquidcrystals, carbon nanorods, inorganic nanorods (e.g., nanorods formed ofzinc oxide, tungsten oxide, indium phosphide, cadmium selenide and/orlead sulphide), or polymers containing moieties capable of acceptingelectrons or forming stable anions (e.g., polymers containing CN groupsor polymers containing CF₃ groups), and combinations thereof. In someembodiments, at least some of the polymer dyes in photoactive layer 250have a different color. For example, photoactive layer 250 can includeat least three polymer dyes, each having a different color. In certainembodiments, each of the polymer dyes has a different color.

Examples of polymer organic photovoltaic cells are described, forexample, in U.S. Patent Application Publication No. 2004/0187911, andco-pending an commonly owned U.S. Ser. No. 60/576,033, both of which arehereby incorporated by reference.

Multiple polymer organic photovoltaic cells can be electricallyconnected (e.g., as described above).

The following examples are illustrative and not intended to be limiting.

EXAMPLE 1

Three dye solutions were prepared and tested for their PV performance:(1) 24 mM of Z907 in GBL/MP (1:10 vol./vol.), (2) 40 mM of Z907 inGBL/MP/PPG (1:5:2 vol./vol./vol.), and (3) 40 mM of Z907 in GBL/MP (1:5vol./vol.) with 12 wt % fumed silica. Specifically, the dye solutionswere prepared by dispersing Z907 and optionally fumed silica powder intoa mixture of solvents at the above-mentioned concentrations. Thesolutions were then heated to 80° C. and/or ultrasonicated until allsolids were well dispersed in the solutions. Sintered TiO₂ coating witha thickness of about 12 μm and a surface area of about 70 m²/g was dyedwith the above three dye solutions at room temperature for certainperiods of times and then rinsed by ethanol. The dyeing time wasmeasured from the application of a dye solution on the TiO₂ coating tothe rinsing of the TiO₂ coating by ethanol. The dyed TiO₂ coating wasthen used to prepare photovoltaic cells.

The results showed that, for each of these three dye solutions, 65 mg ofZ907 was absorbed onto 1 g of TiO₂ in about 5 minutes or less. Inparticular, 65 mg of Z907 in dye solution (3) was absorbed onto 1 g TiO₂in about 1 minute. Further, the results showed that including athickening agent (i.e., PPG or fumed silica) in a dye solution did notadversely change the efficiency of the photovoltaic cell. Thephotovoltaic cells prepared from the above three dye solutions allexhibited about 3.0% efficiencies.

EXAMPLE 2

Two dye solutions were prepared and tested for their thermal stability:(1) 24 mM of Z907 in GBL/MP (1:10 vol./vol.) without CAB-O-SIL TS-720silica, and (2) 40 mM of Z907 in GBL/MP (1:5 vol./vol.) with 1 wt %CAB-O-SIL TS-720 silica. The dye solutions were then used to preparephotovoltaic cells in a manner similar to that described in Example 1.The photovoltaic cells thus obtained were then aged at 70° C. for 500hours.

The results showed that the photovoltaic cell without CAB-O-SIL TS-720silica exhibited about 24% loss in efficiency, while the photovoltaiccell containing 1 wt % CAB-O-SIL TS-720 silica exhibited only about 15%loss in efficiency.

Other embodiments are in the claims.

1. A formulation, comprising: cis-RuLL′(NCS)₂, wherein L comprises afirst 2,2′-bipyridyl and L′ comprises a second 2,2′-bipyridyl, and anorganic solvent comprising a mixture of g-butyrolactone and1-methoxy-2-propanol.
 2. The formulation of claim 1, wherein the first2,2′-bipyridyl is the same as the second 2,2′-bipyridyl.
 3. Theformulation of claim 1, wherein L comprises 4,4′-dicarboxylicacid-2,2′-bipyridyl and L′ comprises 4,4′-dinonyl-2,2′-bipyridyl.
 4. Theformulation of claim 1, wherein the formulation comprises about 5 mMcis-RuLL′(NCS)₂.
 5. The formulation of claim 1, wherein the formulationcomprises about 30 mM cis-RuLL′(NCS)₂.
 6. The formulation of claim 1,wherein the formulation comprises about 60 mM cis-RuLL′(NCS)₂.
 7. Theformulation of claim 1, further comprising a thickening agent.
 8. Theformulation of claim 7, wherein the thickening agent comprises fumedsilica particles or poly(propylene glycol).
 9. The formulation of claim8, wherein the fumed silica particles are hydrophobic.
 10. Theformulation of claim 8, wherein a surface of the fumed silica particlesis modified with poly(dimethyl siloxane) moieties.
 11. The formulationof claim 8, further comprising about 1 wt % to about 20 wt % of thefumed silica particles.
 12. The formulation of claim 8, furthercomprising about 12 wt % of the fumed silica particles.
 13. Theformulation of claim 1, wherein g-butyrolactone and 1-methoxy-2-propanolare mixed at a ratio of about 1:5 vol./vol. to about 1:10 vol./vol. 14.The formulation of claim 13, further comprising fumed silica particles.15. The formulation of claim 14, wherein the formulation comprises about1 wt % to about 20 wt % of the fumed silica particles.
 16. Theformulation of claim 14, wherein the formulation comprises about 12 wt %of the fumed silica particles.
 17. The formulation of claim 1, furthercomprising poly(propylene glycol).
 18. The formulation of claim 17,wherein g-butyrolactone, 1-methoxy-2-propanol, and poly(propyleneglycol) are mixed at a ratio of about 1:5:2 vol./vol./vol.
 19. Theformulation of claim 1, wherein the formulation comprises at least about5 mM cis-RuLL′(NCS)₂.
 20. The formulation of claim 1, wherein theformulation comprises at least about 30 mM cis-RuLL′(NCS)₂.
 21. Theformulation of claim 1, wherein the formulation comprises at least about60 mM cis-RuLL′(NCS)₂.
 22. A method, comprising: disposing a formulationcomprising cis-RuLL′(NCS)₂ and a first organic solvent on a firstmaterial to form a photoactive layer, wherein L comprises a first2,2′-bipyridyl, L′ comprises a second 2,2′-bipyridyl, and the firstorganic solvent comprising a mixture of g-butyrolactone and1-methoxy-2-propanol; disposing the photoactive layer between twoelectrodes to provide a photovoltaic cell.
 23. The method of claim 22,wherein the first 2,2′-bipyridyl is the same as the second2,2′-bipyridyl.
 24. The method of claim 22, wherein L comprises4,4′-dicarboxylic acid-2,2′-bipyridyl and L′ comprises4,4′-dinonyl-2,2′-bipyridyl.
 25. The method of claim 22, wherein theformulation further comprises a thickening agent.
 26. The method ofclaim 25, wherein the thickening agent comprises fumed silica particlesor poly(propylene glycol).
 27. The method of claim 25, furthercomprising substantially removing the thickening agent by washing thephotoactive layer with a second organic solvent.
 28. The method of claim27, wherein the second organic solvent is an alcohol.
 29. The method ofclaim 22, wherein 65 mg of the cis-RuLL′(NCS)₂ is absorbed onto 1 g ofthe first material in at most about 5 minutes.
 30. The method of claim22, wherein 65 mg of the cis-RuLL′(NCS)₂ is absorbed onto 1 g of thefirst material in at most about 3 minutes.
 31. The method of claim 22,wherein 65 mg of the cis-RuLL′(NCS)₂ is absorbed onto 1 g of the firstmaterial in at most about 1 minute.
 32. The method of claim 22, whereinthe first material comprises a semiconductor material or an electronacceptor material.